In many operations, particularly oil field operations, pipelines are used to transport multiphase mixtures. In oil fields, such pipelines may be used to transport gas, oil and water mixtures produced from individual oil wells to common gathering lines and to transport gas, oil and water mixtures recovered from a common gathering point to a treatment facility such as a separator or the like. In such instances, the multiphase mixtures frequently tend to separate during transportation to the pipeline so that there are intermittent slugs of liquid followed by slugs of gas and the like. The formation of such slugs in pipelines results in severe stress on the pipelines and erratic operation of the equipment into which the pipelines discharge. As a result, it has been necessary to over-design pipelines to withstand the vibrational stresses and other stresses imposed on the pipelines by the slugs and to over-design separators and other equipment to accommodate the presence of the slugs. Such lines are also susceptible to fatigue failure as a result of the vibrational and other stresses.
The stresses on the pipeline can result from forces generated at bends in the pipeline as well as other mechanical stresses imposed on the pipeline by the multiphase mixture. For instance, the force imposed on the pipeline at a bend can be generally characterized by the equation EQU F=PQV
wherein F equals the force imposed upon an elbow of the pipe; P equals the density of the mixture; Q equals the volumetric flow rate; and V equals the stream velocity. Since the densities of gas and water or oil are radically different, it is clear that radically different forces are imposed on the pipeline elbow intermittently when slugs are present in the line. These intermittent forces impose stresses which result in fatigue failure, vibration, and the like which have resulted in increased maintenance and replacement requirements for pipelines used to transport multiphase mixtures and over-design of such pipelines in an attempt to reduce the increased maintenance and replacement requirements.
Accordingly, methods have been sought to control slugs in pipelines transporting multiphase mixtures.